‘The Watch” is a comedy about a baffling and revolting alien life-form: Ohioans. By extension, the joke is on any American striver who doesn’t have a groovy urban job. This time, when audience members walk out saying, “It slimed me,” they won’t be quoting from the movie, but simply expressing an unpleasant experience.

Just as Tom Hanks figured “halfway to Gump” was about the right mental setting to play a Walmart-type manager in last year’s “Larry Crowne,” Ben Stiller plays an Ohio Costco manager slightly hunched over with dullness, wearing Fred Rogers clothes, bragging about his loser habits and saying things like, “I don’t have any black friends yet, but I am in the market.”

This quiet and frustrated dork, you see, is the movie’s idea of what a lame suburban middle-aged man is like, and in case you don’t get the joke, Vince Vaughn, Jonah Hill and Richard Ayoade are there to repeat it, in every scene, as an irresponsible dork, a wannabe-cop dork and a British dork, respectively.

Hollywood is telling us how pathetic are these minor mortals who sell and buy the $5.99 DVDs that pay for their overlords’ houses in the LA hills . . . yet these are the same geniuses who keep giving us the likes of “John Carter” and “Battleship.”

And “Hot Rod,” the busted Andy Samberg vehicle that is the only previous film from director Akiva Schaffer. At Costco, being responsible for this kind of cleanup in aisle 6 would earn you a firing. In Hollywood? A promotion.

In “The Watch” (originally “Neighborhood Watch” but retitled after the Trayvon Martin killing), Stiller’s manager forms a neighborhood watch group (matching sateen jackets with a tiger logo) to investigate a strange attack at Costco that killed his Latino security guard. The guard gets ripped to shreds by an alien monster, which I guess is funny because he’s an immigrant, and his death yields a comedy snippet of “The Sound of Silence” in Spanish. Get it? Spanish. Funny language. Commonly associated with those hilarious working people, somewhere down there.

Will Forte pops up as a cop in a silly mustache, which tells you all you need to know about Will Forte’s comedy, and he hassles Stiller’s crew as they spend their evenings pleading with the townsfolk for support (in nerdy No More Murders sweatshirts that seem particularly unfunny this week, not that it could ever have been funny) or getting pelted with eggs by teens (“Yolk’s on you,” someone calls out). Vaughn is shown being awed by a nesting doll and a 3-D television set.

There are occasional encounters with aliens, but Schaffer is hardly a master of thrills, so the “action” scenes come across as brief, noisy periods of rest from the lame comedy, which counts for something, if not quite what the filmmakers intended. Instead of being a cool sci-fi flick that’s also got cool guys cracking wise, à la “Ghostbusters,” “The Watch” is stuck with a group of half-wits the screenwriters obviously don’t find interesting. (The writers are Jared Stern, along with Seth Rogen and Evan Goldberg, the “Superbad” collaborators whose previous work never stooped to this level.)

The plot is aimless, wandering away from the main story to, for instance, an orgy scene and a subplot about one guy’s inability to get his lady pregnant. Half-hearted bits about other townsfolk (Billy Crudup as an oddball neighbor, “Full Metal Jacket” sarge R. Lee Ermey as a redneck) succeed only in diluting the unfunny — if it’s possible to water down water. Only Hill manages to bring a little life to his part, a misfit who lives with his mom. As is often the case with him, his best stuff is so Jonah Hill-ish I have a hunch he improvises a lot of it.

At last we get down to business with the aliens, without even rudimentary rules having been established prior to the expensive-looking yet perfunctory battle (are the aliens hard to kill or ridiculously easy? It depends). Ninety percent of the budget seems to have been saved up for the last 10 minutes, but it’s far too late to get us involved. The danger of dreaming up a predictable adventure for a group of nobodies you hold in contempt is that the audience will see your indifference and raise you.